When people say oil "prices" they typically mean crude oil futures. Crude oil futures are contracts for the future delivery/sale of a certain specification of oil at a certain location. In the case of WTI, widely considered the main US benchmark and most liquid commodity futures contract in the world, that specification is crude that meets the specs outlined here:

https://www.cmegroup.com/content/dam/cmegroup/rulebook/NYMEX/2/200.pdf

and is delivered into tanks in Cushing, Oklahoma.

Every month futures prices are tied to the physical supply and demand situation in the US because if futures prices get too expensive/cheap relative to the futures people will buy/sell crude and deliver it to Cushing. For example, say a ton of speculation drives futures to 120/bbl 3 weeks before contract expiration but there is actually tons of physical crude available and the price really shouldn't be that high. Say prices in Midland, Texas are only 90/bbl and this reflects the "real" price of physical crude based on what people around the world are willing to pay for physical barrels. Crude shippers/traders will start buying crude in Midland while simultaneously selling futures for delivery in Cushing. By doing so, those traders just locked in a 30/bbl profit minus whatever is costs to get the crude from Midland to Cushing and store it for a couple weeks. They will then ship their crude to Cushing, wait 3 weeks, and delivery against the sale contract that they agreed to at 120/bbl. You can see how in aggregate everyone doing this will bring down that futures price from 120/bbl to roughly 90/bbl.